A cellular communication system is an interference limited system. Since identical spectral resources are reused in adjacent or close-by cells, system performance is restricted by inter-cell signal interferences to a large extent. A future cellular communication system is required to provide higher spectral efficiency and cell-edge throughput, while inter-cell interference (ICI) must be reduced in order to achieve this goal.
In-depth research on how to reduce inter-cell interference has been done in the current process of standardization for LTE (long term evolution), and a so-called “loose” cooperation mode has been basically agreed to be adopted, which is to exchange some simple information through an X2 interface among cells in order to achieve cooperation on resources of adjacent cells (transmitting power, resource blocks used and so on) and thereby achieving the goal of reducing inter-cell interference. Since the information transmission speed that can be admitted over X2 interface is relatively low and the time delay of information exchange is relatively big, the system performance gain induced by adopting this inter-cell “loose” cooperation mode is very limited.
Compared with the inter-cell “loose” cooperation, a more effective cooperation mode is a “tight” cooperation, that is, inter-cell joint signal transmission. Inter-cell “tight” cooperation mode can transform the signal interference among conventional cells that do not adopt cooperation into a useful signal, and thereby enhances the system performance effectively. For the detailed implementation of the technique, please refer to M. K. Karakayali, etc. “Network coordination for spectrally efficient communication in cellular systems” IEEE wireless commun. Mag, August 2006.
However, current research on “tight” cooperation is still in the theoretical research phase, and it has not been able to present a practical and feasible method yet against requirements for a practical system design, such as signaling overhead, implementation complexity and so on.